Imagine a bomb that explodes when light hits its inbuilt sensor. Imagine that you have one hundred of these bombs: an unknown number of the bombs are duds and nothing happens when you shine light on them; the others are fully working. Obviously if you shine light on each one you discover which are duds, but then you are left with duds and the remains of exploded bombs.
Scientists discovered that quantum theory allows you to determine which bombs are duds without exploding them. Welcome to the world of interaction-free measurements.
A photon from a laser hits an angled silvered mirror and either goes through the mirror in a straight line or reflects at 90 degrees. According to quantum theory, the photon does both at the same time as dual probabilities. These probabilities "inspect" the bomb without triggering it, revealing useful information.
The problem is that half the time, if it's not a dud, the bomb really explodes, but this can be reduced by using the Zeno effect.
They also discovered that you can get a quantum computer to make a calculation without turning it on.
https://johncarlosbaez.wordpress.com/2013/08/24/the-elitzur-vaidman-bomb-testing-method/
